Polymer liquid crystal (PLC) macromolecules consisting of LC and flexible sequences are considered, particulary at the phase transition LC-i from an anisotropic to the isotropic phase. The Flory lattice model is used for formulation of the partition function; the orientation distribution function for LC interactions introduced by Flory and Ronca is included. While Flory and collaborators have improved the original Flory theory by taking into account the Maier and Saupe molecular mean field theory of liquid crystallinity, we now use the Landau approach for calculating the Helmholtz function of the system as a function of the orientation parameter s. This leads to formulas for parameters of the model in the vicinity of the LC-i transition. The critical values at the transition of the strength of orienting interactions s, the system temperature, and the anisotropy of LC sequences are calculated and discussed. The treatment is limited to monodisperse systems.